Tunable resonant structure



y 1954 w. SCHREINER TUNABLE RESONANT STRUCTURE 2 Sheets-Sheet l Filed July 11, 1951 INVENTOR. Louis W. Schreiner Patented July 13, 1954 TUNABLE RESONANT STRUCTURE Louis W. Schreiner, Park Ridge, 111., assignor to Raytheon Manufacturing Company, a corporation of Delaware Application July 11, 1951, Serial No. 236,231

1 3 Claims.

This invention relates in general to resonant tuning systems, and more particularly to a tunable resonant structure adaptable for use in a distributed constant radio frequency tunable resonant circuit.

In ultra high radio frequency systems, the tuning structure comprises cylindrically shaped conductors which are expensive to manufacture, since they do not lend themselves to punch press operations.

In certain systems wherein it is desired to avoid the use of sliding contacts at the high current end, tuning the higher frequencies of the band causes the inner conductor to extend outward from the hollow outer conductor, thereby requiring greater space for operation.

Accordingly, an important object of the present invention is to provide a tunable resonant structure adaptable for use in distributed constant radio frequency circuits that would be compact and occupy a minimum of space by providing a variably positioned flexible ribbon conductor that bends into a reverse direction outside of a hollow conductor to form substantially parallel-spaced portions thereof.

Another object of the present invention is to provide a tunable resonant structure adaptable for use in distributed constant radio frequency circuits that is economical to manufacture, since component parts thereof lend themselves to punch press operations.

Another object of the present invention is to provide a tunable resonant structure adaptable for use in distributed constant radio frequency circuits that minimizes contact noises by providing a short bar fixedly secured to a hollow conductor and having a contacting surface at one end thereof extending interiorly of the hollow conductor for engaging a movable conductor.

Other objects and features will appear upon further perusal of the detailed description taken in conjunction with the accompanying drawings in which:

Fig. 1 is a perspective view of the novel tuner structure embodied in the present invention;

Fig. 2 is a sectional view taken substantially along the line 2, 2 of Fig. 1; and

Fig. 3 is a schematic drawing illustrating a preferred tunable resonant circuit utilizing the novel tuner structure embodied in the present invention.

According to the invention, a tunable resonant structure is herein provided adaptable for use in a distributed constant tunable resonant circuit comprising a flexible ribbon conductor or a thin metallic conducting strip made of suitable conductor material, such as Phosphor bronze, and a hollow member or conductor, which in the preferred embodiment has substantially a rectangular cross section.

For variably positioning or disposing the ribbon conductor in the hollow conductor in order to select a resonant frequency for the tuning system, ribbon driving means, such as a pulley arrangement, is herein provided. The flexible ribbon conductor forms a portion of an endless band for the pulley arrangement and bends in a contour conforming to the contour of a driving wheel of the pulley arrangement. The portion of the flexible ribbon conductor not used in a particular conducting circuit extends out of the hollow conductor in a substantially parallelspaced relationship to the portion thereof used in the conducting circuit. This provides a compact unit in that the portion thereof not used in a particular conducting circuit is not extending axially outward from the hollow conductor. The length of the portion of the ribbon conductor in the hollow conductor determines the resonant frequency of the tunable resonant circuit.

For preventing chattering or contact noises, a fixedly secured shorting bar is attached at one end of the chamber conductor and extends therein a suitable distance. The other end of the shorting bar is provided with a contacting surface for cooperatively engaging the flexible ribbon conductor. Since the short end of a transmission line is the high current side, extending the contacting surface of the shorting bar projection interiorly into the hollow conductor tends to eliminate undesirable chatter or contact noises. It is apparent, therefore, that the shorting bar could be eliminated and have the end portion of the hollow conductor form the contacting surface for cooperative engagement with the flexible ribbon conductor.

It is to be noted that the tuning structure is operative with one flexible ribbon conductor, however, the present invention also provides a plurality of flexible ribbon conductors variably positioned in a single hollow conductor by means of a single pulley arrangement. The use of two flexible ribbon conductors in a single hollow conductor enables the use of a balanced tuning structure for use with balanced inputs, such as an antenna input. In a balanced tuning structure, the hollow member acts functionally as a shield.

Referring now to Figs. 1 and 2, a hollow outer member [0 or conductor is herein provided having in its preferred embodiment a cross section substantially of a rectangular configuration and made of suitable conducting material, such as brass. The advantages gained by such an outer conductor is that all parts thereof lend theznselves to punch press operations, and therefore are more economically manufactured.

For providing a shorted end for the tuning structure, a shorting bar mounting bracket II is attached to one end of the hollow conductor I0 by suitable means, such as screws. When desired, the mounting bracket II may be integrally formed with the hollow conductor II]. At the opposite end of the hollow conductor III is an open end section I2 for the tuning structure.

It is to be noted that the tuning structure here'- in provided in the preferred embodiment is of the wave length transmission line type. However, the invention and principles disclosed herein may be readily adaptable for use in wave length transmission lines or any similar system. The application hereof may be somewhat similar to that of coaxial type transmission lines.

For selecting the resonant frequency of the tuning structure, variably positioned flexible ribbon or flexible metallic strip inner conductors I3 and I4 are herein provided which are made of suitable conducting material. such as Phosphor bronze, and which are variably disposed in the hollow member or conductor I I]. In the event a balanced tuning structure is desired for a balanced input, such as an antenna input, a plurality of flexible ribbon conductors, such as I3 and I4 strips, is used. However, a single flexible ribbon conductor, such as either I3 or I4 strips, may be used in the event a circuit design does not require a balanced tuning structure. When a balanced tuning structure is used, insulating material IIa is placed between the mounting bracket II and the chamber II]. However, when a single inner conductor is provided, no insulating material such as Ila is required. In the balanced tuning structure, the chamber III is considered functionally as a shield.

In order to position or dispose the flexible ribbon conductors I3 and I4 into the hollow conductor III, a novel pulley arrangement or ribbon driving means is herein provided.

The ribbon driving means or pulley arrangement comprises a suitable drive pulley wheel mounting bracket I5, which is attached to the shorted endof the hollow conductor II) by suitable means, such as screws, not shown. The mounting bracket I5, when desired, can be integrally formed with the hollow conductor III. In order to provide a rotatable support, a driving shaft I6 is received by suitable apertures I? in the mounting bracket I5. Secured to the driving shaft I6 is a pulley driving wheel or drum I8,

which is made of suitable material, such as nonconductive material. When desired, the shaft 56 and pulley driving wheel I8 may be integrally formed.

At the open end I2 of the hollow conductor II! is provided a suitable string pulley wheel mounting bracket I9 which is attached to the hollow conductor III by suitable means, such as screws, not shown. The string pulley wheel mounting bracket may be integrally formed with the hollow conductor II), when desired.

In order to provide a rotatable support, a string pulley wheel shaft 20 is received by suitable apertures 2I in the mounting bracket I9. Secured. to the string wheel shaft is a string pulley wheel or drum 22, which is made of suitable material, such as a non-conductive material. When desired, the shaft 20 may be integrally formed with the wheel 22.

Endless bands for the pulley arrangement comprise the flexible ribbon conductors I3 and I4. For maintaining adequate tension in the band, biasing springs 23 and 24 are attached at one end thereof to the ribbon conductors I3 and I4 and at the other end thereof are attached to suitable insulated connecting means, such as strings 25 and 26.

For rotating the band in order to provide variable positioning or disposing of the flexible ribbon conductors I3 and I4 into the hollow memher or conductor I0, a suitable turning device, such as a knob, not shown, is secured to the driving shaft I6 for rotating the wheel it, which in turn cooperatively engages the flexible ribbon conductors I3 and I4 for movement thereof.

In order to prevent slippage between the wheel I8 and the ribbon conductors I3 and It, suitable raised surfaces or pins 21 are provided on the wheel I8 which are cooperatively received by in dentations or apertures 28 of the ribbon conductors I3 and I4.

To prevent lateral slippage between the wheel 22 and the strings 25 and 2B, the strings 25 and 25 are suitably received by means such as circular grooves 28 in the wheel 22.

In order to prevent chattering or contact noises at the high current end of the tuning structure, which is the shorted end of the tuning structure, shorting contact bars or lateral extensions 33 and SI are fixedly attached at one end to the shorting bar mounting bracket II by suitable means, such as screws, and are extended interiorly into the chamber III a suitable predetermined dis tance. At the other ends of the shorting bars 33 and SI are provided the contacting surfaces and 32a which cooperatively engage the flexible ribbon conductors I3 and I4.

It is to be noted that the contacting surface could be provided at the surface surrounding an aperture 33 of the mounting bracket II which receives the flexible ribbon conductors I3 and I4 therethrough.

A cover 35 is provided to form the upper surface of the hollow conductor II) and is attached thereto by suitable means, such as screws, not shown, which are received by apertures 36 of the hollow conductor flanges 31.

In operation, the selected resonating frequency of the tuner structure is determined by the length each of the flexible ribbon conductors, such as I3 and I4, in the hollow conductor or member as extended interiorly of the hollow conductor II! from the shorted end II thereof. Since the preferred embodiment is a wave length transmission line, the length of each of the inner conductors I3 and I4, as determined from the shorting bar mounting bracket II, is one quarter of the wave length of the selected resonant frequency. Therefore, as the determined length of each of the inner conductors I3 and I4 decreases, the selected resonant frequency of the tuning structure increases, and the converse is also true.

Thus, for selecting the resonant frequency of the tuning structure, drive shaft I6 is rotated and rotating therewith is the drive wheel I3. As the drive wheel I8 revolves, the flexible ribbon conductors I3 and I4 cooperatively engage the drive wheel I8 for movement therewith.

The strings 25 and 26 forming endless bands with the flexible conductors I3 and I4 rotate the string pulley wheel 22, which imparts move ment to the shaft 20.

The conductors I3 and I4 are flexible ribbons and therefore the portions thereof that engage the drive wheel I8 assume the semicircular configuration of the contacting portion of the drive wheel I8. Hence, when a resonant frequency is selected, the portions of the conductors I3 and I I that are outside of the hollow conductor I0, and therefore not a conducting portion of the resonant structure, are deflected into a reversed direction and assume a parallel-spaced relationship to the portions of the flexible conductors l3 and i l that are a part of the conducting portion of the resonant structure. Thus, the non-conducting portions of the conductors i3 and l-i do not extend axially from the hollow member l0, and thereby provide a compact tuning structure that occupies a smaller space.

The tuning structure as incorporated in a distributed con tant radio frequency tunable resonant circuit may be coupled to other stages by suitable means, such as well-known coupling loops, which will be described in more detail in reference to Fig. 3, or direct wiring connections.

Referring now to 3 for a preferred tuning circuit utilizing the novel tuning structure of the present invention, the circuit includes a preselector 38 which is connected to a balanced antenna coupling 39 by suitable means such as antenna input loop it. The antenna input loop consists of a suitable wire bent into the shape of a loop. The preselector 38 has the physical structure of the balanced tuning structure of the type heretofore described in detail in reference to Figs. 1 and 2. More specifically, the balanced tuning structure comprises the flexible ribbon conductors l3 and it with the hollow member ill functioning as a shield.

The preselector 38 operates as a filter with a very high Q; with the output thereof being applied through a coupling loop ll to a converter tuning structure 52. The coupling loop 2! consists of suitable wire bent into the shape of a loop. One end thereof is directly attached to the member ll of preselector 38, and the other end thereof is directly attached to the member ii of the converter tuning structure 12. The intermediate portions thereof do not engage the conductor it, but pass through a suitable aperture a, shown in Fig. 1. The converter tuning structure it has the physical structure of the tuning structure heretofore described in detail in reference to Figs. 1 and 2. However, in the converter tuning structure 22, only one flexible ribbon conductor, such as either 13 or is, is used and there is no insulating material such as I la.

A line tuned oscillator stage 43 is herein provided which includes a transmission line i l having a suitable duo-diode type tube d5 operatively connected thereto. A sliding short is is variably adjustable on the transmission line t l to select the oscillatory frequency. Shield s1 is provided for the transmission line A l. The transmission line i l terminates into resistors Q8 and 49.

The output from the oscillator s3 is applied through oscillation injection condenser 50 to a mixing crystal 5i of the converter d2. For providing an intermediate frequency output, the crystal 5! mixes the oscillating frequency and the preselected radio frequency from the converter tuning structure 12. Inductance coil 52 is provided for decoupling purposes, and is directly attached to the shorting member 3! by suitable means such as wire, which is suitably received by aperture iaia. The intermediate frequency is fed to a conventional low noise intermediate frequency amplifier 5-3. By-pass condenser 55 provides a radio frequency by-pass means.

Another conventional intermediate frequency amplifier 55 interconnects a conventional detector 56 and the low noise intermediate frequency amplifier 53.

An audio circuit is connected to the detector 5E and comprises a conventional audio amplifier 5? and a sound producing device 58. A video cir cuit is connected to the detector and com prises a conventional Video amplifier 55 and pic ture producing tube 55.

It is apparent that variations and modifications be effected without departing from the scope of the appended claims.

I claim:

1. A. tunable resonant structure for use in a distributed constant radio frequency circuit comprising combination, a transmission line comprising a plurality of conductors at least one of which is a flexible ribbon, means for selecting the resonant frequency of tuning structure comprising means for producing substantially a short circuit between said conductors at a predetermined point, and means for moving said flexible conductor with respect to said point conip a pulley arrangement supporting an endless band or which said flexible conductor forms a portion.

2. A tunable resonant structure for use in a distributed constant radio frequency circuit compri 'ng in combination, a transmission line comprising plurality of conductors at least one of which is a flexible ribbon, means for selecting the resonant frequency of said tuning structure comprising means for producing substantially a short circuit between said conductors at a predete mined point, and means for moving said flexible conductor with respect to said point comprising a pulley arrangement supporting an endless band of which said flexible conductor forms a portion, said flexible ribbon being an inner conductor of said transmission line and having a portion thereof surrounded by another of said conductors spaced therefrom, said portion having a terminating end within said surrounding conductor.

3. A tunable resonant structure for use in a distributed constant radio frequency circuit comprising in combination, a transmission line comprising a plurality of conductors at least one of which is a flexible ribbon, means for selecting the resonant frequency of said tuning structure comprising means for producing substantially a short circuit between said conductors at a predetermined point, and means for moving said flexible conductor with respect to said point comprising a pulley arrangement supporting an endless band of which said flexible conductor forms a portion, said flexible conductor being one of a plurality of flexible conductors having portions and terminating ends positioned inside and movable with respect to a shielding member surrounding said portions.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,035A35 Crossley Mar. 24, 1936 2,117,090 Grundmann May 10, 1938 2,175,710 Usselman Oct. 10, 1939 2,203,481 Zottu June l, 1940 2,292,254 Van Beuren Aug. 4, 1942 2,467,758 Lindenblad Apr. 19, 1949 2,488,545 Lader Nov. 22, 1949 2,573,045 Murphy Oct. 30, 1951 2,581,680 Martenot Jan. 8, 1952 FOREIGN PATENTS Number Country Date 541,380 Great Britain Nov. 25, 1941 594,622 Great Britain Nov. 14, 1947 

